Closed-loop Control Using High Power Hexapole Magnetic Tweezers for 3D Micromanipulation

This paper presents the design, modeling, integration, and application of 3D printed high power hexapole magnetic tweezers for 3D micromanipulation applications. Six sharp-tipped magnetic poles were configured with electromagnetic coils and mounted on 3D printed magnetic yokes to form a tilted Cartesian coordinate system for actuation. A closed loop control algorithm was developed to automatically manipulate external power supplies connected to the magnetic tweezers, by using 3D positional information obtained from real-time image processing techniques. When compared against other designs of magnetic tweezers, our system has a larger working space and can generate higher magnetic field strengths. This allows for more diverse applications regarding small scale manipulation, including cell manipulation and cell therapy. Experiments and analytics explained in this paper demonstrate the closed-loop manipulation of micro-swimmers can provide a magnetic force as high as 800 pN while maintaining a positional error below 4 µm in 3D and 1.6 µm in 2D. Using the desired location as the control input, the microswimmers investigated were able to achieve arbitrary 2D and 3D trajectories. We also show that the implemented hexapole magnetic tweezers have adequate power to control microswimmers in Newtonian fluid environments. The system will later be optimized and deployed to control microswimmers in non-Newtonian fluid environments.